A thin-film transistor (hereinafter also referred to as “TFT”) using amorphous silicon generates a photocurrent when light enters a semiconductor layer thereof, and therefore, in recent years, a display panel with a touch panel function that uses TFTs not only as switching elements for respective pixels, but also as photosensor elements has been proposed.
Patent Document 1, for example, discloses an optical sensor device in which an amorphous silicon photodiode and an amplifier constituted of a thin-film transistor are integrally formed on a substrate.